无法使用Iterator迭代List，但在每个迭代器上使用都可以正常工作

Question

Populating the Question Bean with Answer Bean from applicationContext.xml and error is thrown when am iterating List of Answer using Iterator, but working fine with For Each loop.

 {        


<bean id="answer1" class="com.core.spring.Answer">  
<property name="id" value="1"></property>  
<property name="answerText" value="Java is a programming language"></property>  
<property name="by" value="Ravi Malik"></property>  
</bean>  
<bean id="answer2" class="com.core.spring.Answer">  
<property name="id" value="2"></property>  
<property name="answerText" value="Java is a platform"></property>  
<property name="by" value="Sachin"></property>  
</bean>  

<bean id="answer3" class="com.core.spring.Answer">  
<property name="id" value="3"></property>  
<property name="answerText" value="Java is a platform"></property>  
<property name="by" value="Sachin"></property>  
</bean>  

<bean id="question" class="com.core.spring.Question">
<property name="id" value="1"></property>
<property name="questionText" value="What is Java?"></property>
<property name="answers">
<list>
<ref bean="answer1"/>
<ref bean="answer2"/>
<ref bean="answer3"/>

</list>
</property>
</bean>

}

This is the Bean Class of Question.

{
  package com.core.spring;

    import java.util.ArrayList;
    import java.util.Iterator;
    import java.util.List;

    public class Question {

        private int id;
        String questionText;
        List<Answer> answers=new ArrayList<Answer>();


        public int getId() {
            return id;
        }
        public void setId(int id) {
            this.id = id;
        }
        public String getQuestionText() {
            return questionText;
        }
        public void setQuestionText(String questionText) {
            this.questionText = questionText;
        }
        public List<Answer> getAnswers() {
            return answers;
        }
        public void setAnswers(List<Answer> answers) {
            this.answers = answers;
        }

        public void displayInfo(){

            System.out.println("Question: "+id);
            System.out.println(questionText);
            System.out.println("Answers");

            for(Answer ans:answers){
                System.out.print(ans.getId());
                System.out.println(": "+ans.getAnswerText());
            }

            for (Iterator<Answer> ans = answers.iterator(); ans.hasNext();){
                System.out.print(ans.next().getId());
                System.out.println(": "+ans.next().getAnswerText());

            }
            /*Iterator<Answer> ans=answers.iterator();
            while(ans.hasNext()){
                System.out.print(ans.next().getId());
                System.out.println(": "+ans.next().getAnswerText());
            }*/
        }

    }**

}

Answer 1

Your use of the Iterator is wrong - next() moves the iterator to the next position, and you're calling it twice from the while loop's body, and only cheking hasNext() once.

You should only call next() once, extract its value to a local variable and use it how many times you need:

Iterator<Answer> ans = answers.iterator();
while(ans.hasNext()) {
    Answer answer = ans.next();
    System.out.print(answer.getId());
    System.out.println(": " + answer.getAnswerText());
}

Answer 2

That loop should be like this

 for (Iterator<Answer> ans = answers.iterator(); ans.hasNext();){
                Answer ans = ans.next();
                System.out.print(ans.getId());
                System.out.println(": "+ans.getAnswerText());

            }

You are calling next() method in each System.out.println()

 for (Iterator<Answer> ans = answers.iterator(); ans.hasNext();){
                System.out.print(ans.next().getId());  //moving one element
                System.out.println(": "+ans.next().getAnswerText());  //moving one element

            }

Which obviously leads to odd results while printing them.